1. Field of the Invention:
This invention relates to the reaction of long-chain fatty alcohols with polyphosphoric acid to form monoalkylphosphoric acid esters and to their separation from the orthophosphoric acid formed during the reaction.
2. Statement of Related Art:
Monoalkylphosphoric acid esters (monoalkylphosphates) are industrially produced by reaction of alcohols with phosphorus oxychloride. G. Imokawa "Journal of the American Oil Chemists' Society", 55, 839 (1979) describes a corresponding solvent-free reaction. On completion of the reaction, excess phosphorus oxychloride is hydrolyzed by addition of water and the phosphoric acid formed is separated off by ether/water extraction.
British patent 1,475,109 describes a process for the reaction of alcohols with phosphorus oxychloride in a ration of 1.1 moles of phosphorus oxychloride per mole of starting material (alcohol), the reaction being carried out in the presence of cycloalkanes and/or alkanes as solvent. This known process is carried out in dilute solutions. Due to the quantity of hydrogen chloride released during the reaction (3 moles/monoalkylphosphate), the process has to satisfy particular technological requirements. According to GB 1,475,109, the presence of solvents is necessary to avoid secondary reactions, such as for example the formation of diesters. Accordingly, the reaction to produce monoalkylphosphates is carried out in a very large quantity of cyclohexane.
According to Ullmanns Encycklopadie der technischen Chemie, 4th Edition, Vol. 18, page 389, monophosphoric acid esters are formed in addition to free phosphoric acid in the reaction of the alcohols with polyphosphoric acid. The phosphoric acid formed during the reaction is particularly troublesome in cosmetic products, electrolyte solutions, emulsions, and also in the spinning of synthetic fibers.